1. Field of the Invention
The present invention broadly relates to light interruption position detection and, more particularly, is concerned with detection apparatus which includes a pair of linear image detectors, such as charge-coupled devices (CCDs), to sense interruption of a light source for facilitating the determination by associated control circuitry of where, in an X-Y plane, the interruption took place.
2. Description of the Prior Art
One type of conventional apparatus for detecting the light interruption position in an X-Y plane of a psssive object, such as a human finger or a pencil, utilizes an X-coordinate array of multiple light sources mounted along one side of a rectangular display panel and paired with a corresponding X-coordinate array of multiple light detectors mounted on the opposite side of the panel. Also, similar Y-coordinate arrays of paired multiple light sources and detectors are respectively mounted along the remaining two opposite sides of the rectangular panel. Thus, the perimeter of the panel is covered by oppositely paired arrays of light sources and detectors. Examples of such apparatus are disclosed in U.S. Pat. Nos. 3,478,220; 3,764,813; 3,775,560 and 3,860,754.
This type of detection apparatus has certain inherent disadvantages. First, spatial resolution of the apparatus is no better than the limitations imposed by the number, size and spacing of the individual light sources and detectors, one from the next in the respective arrays thereof. Thus, in some commercial equipment of this type, it is possible for the human finger to be placed between two adjacent light sources or two adjacent detectors and be missed by the parallel beams of light provided by the sources. Second, the apparatus utilizes a large number of active elements, i.e., light sources and detectors, not counting the circuitry, which are costly and have to be precisely mounted, in most cases, by manual labor. Therefore, the component cost and cost of manufacture and assembly are high. Third, the excessive number of light sources and detectors necessitates complex and costly arrangements of circuit components to operate the apparatus.